C/C++

Jun

2019

How to fix C warning ‘implicit declaration of function _exit’

Problem:

You have C code like

_exit(1);

but when you try to compile it you see a warning message like

main.c: In function ‘main’:
main.c:3:5: warning: implicit declaration of function ‘_exit’ [-Wimplicit-function-declaration]
     _exit(1);
     ^~~~~
main.c:3:5: warning: incompatible implicit declaration of built-in function ‘_exit’

Solution:

Add

#include <unistd.h>

at the top of the source file where the error occured.

Note that in case you use _Exit(...) (capital E) instead of _exit(...), you need to add

#include <stdlib.h>

instead.

Read the manpage for _exit in case you need further information on _exit(...).

Jun

2019

How to fix C error ‘RTLD_NEXT undeclared’

Problem:

You have C code like

dlsym(RTLD_NEXT, 'myfunc');

but when you try to compile it you see an error message like

main.c:3:11: error: ‘RTLD_NEXT’ undeclared (first use in this function)
     dlsym(RTLD_NEXT, 'myfunc');
           ^~~~~~~~~

Solution:

Add

#define _GNU_SOURCE
#include <dlfcn.h>

at the top of the source file where the error occured.

In order for RTLD_NEXT to be declared, #define _GNU_SOURCE must occur before the first #include statement!

Jun

2019

How to fix C warning ‘implicit declaration of function dlsym’

Problem:

You have C code like

dlsym(RTLD_NEXT, 'myfunc');

but when you try to compile it you see a warning message like

main.c: In function ‘main’:
main.c:3:5: warning: implicit declaration of function ‘dlsym’ [-Wimplicit-function-declaration]
     dlsym(RTLD_NEXT, 'myfunc');

Solution:

Add

#include <dlfcn.h>

at the top of the source file where the error occured. This will include both dlopen, dlsym and related definitions like RTLD_NEXT.

Jun

2019

How to fix C error ‘unknown type name intptr_t’

Problem:

You have C code like

int v = 123;
intptr_t vptr = (intptr_t)&v;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:5:1: error: unknown type name ‘intptr_t’; did you mean ‘__int128_t’?
 intptr_t vptr = (intptr_t)&v;
 ^~~~~~~~
 __int128_t
main.c:5:18: error: ‘intptr_t’ undeclared (first use in this function)
 intptr_t vptr = (intptr_t)&v;
                  ^~~~~~~~
main.c:5:18: note: each undeclared identifier is reported only once for each function it appears in

Solution:

Add

#include <stdint.h>

at the top of the source file where the error occured.

Jun

2019

How to fix va_list/va_arg related C error ‘expected expression before int’

Problem:

You have C code like

va_list ap;
int mode = va_arg(ap, int);

but when you try to compile it you see an error message like

main.c:5:23: error: expected expression before ‘int’
  int mode= va_arg(ap, int);
                       ^~~

Solution:

This error occurs because va_arg is undeclared. Add

#include <stdarg.h>

at the top of the source file where the error occured. This will include the definitions for va_list and the va_arg function.

Jun

2019

How to fix C error ‘unknown type name va_list’

Problem:

You have C code like

va_list ap;
int mode = va_arg(ap, int);

but when you try to compile it you see a warning message like

main.c: In function ‘main’:
main.c:4:2: error: unknown type name ‘va_list’
  va_list ap;
  ^~~~~~~

Solution:

Add

#include <stdarg.h>

at the top of the source file where the error occured. This will include the definitions for va_list and the va_arg function.

Jun

2019

How to fix C warning ‘implicit declaration of function va_arg’

Problem:

You have C code like

va_list ap;
int mode = va_arg(ap, int);

but when you try to compile it you see a warning message like

main.c:5:12: warning: implicit declaration of function ‘va_arg’ [-Wimplicit-function-declaration]
  int mode= va_arg(ap, int);

Solution:

Add

#include <stdarg.h>

at the top of the source file where the error occured. This will include the definitions for both va_list and va_arg.

Jun

2019

How to fix C error ‘mode_t undeclared’

Problem:

You have C code like

mode_t mode;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:4:2: error: unknown type name ‘mode_t’
  mode_t mode;
  ^~~~~~

Solution:

Add

#include <sys/stat.h>

at the top of the source file where the error occured. In case you want further information about what mode_t represents, I recommend reading this blogpost.

Jun

2019

How to fix C error ‘EFAULT undeclared’

Problem:

You have C code like

errno = EFAULT;

but when you try to compile it you see an error message like

main.c:4:5: note: each undeclared identifier is reported only once for each function it appears in
main.c:4:13: error: ‘EFAULT’ undeclared (first use in this function)
     errno = EFAULT;

Solution:

Add

#include <errno.h>

at the top of the source file where the error occured. This will include both error codes like EFAULT and the global errno variable itself.

Jun

2019

How to fix C error ‘errno undeclared’

Problem:

You have C code like

errno = EFAULT;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:4:5: error: ‘errno’ undeclared (first use in this function)
     errno = EFAULT;
     ^~~~~
main.c:4:5: note: each undeclared identifier is reported only once for each function it appears in
main.c:4:13: error: ‘EFAULT’ undeclared (first use in this function)
     errno = EFAULT;

Solution:

Add

#include <errno.h>

at the top of the source file where the error occured. This will include both the errno variable and specific error codes like EFAULT.

Jun

2019

How to fix GCC error ‘implicit declaration of function printf’

Problem:

You have C code like

printf("test");

but when you try to compile it you see a warning like

main.c: In function ‘main’:
main.c:2:5: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
     printf("test");
     ^~~~~~
main.c:2:5: warning: incompatible implicit declaration of built-in function ‘printf’
main.c:2:5: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’

Solution:

Add

#include <stdio.h>

at the top of the source file where the warning occured.

Note that this warning message is just a warning and if you use printf correctly, your program will work even without #include <stdio.h>. However, incorrect usage of printf and similar functions will lead to hard-to-debug errors, so I recommend to add #include <stdio.h> in any case, even if it works without.

Jun

2019

How to fix C error ‘false undeclared’

Problem:

You have C code like

bool mybool = false;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:2:5: error: unknown type name ‘bool’; did you mean ‘_Bool’?
     bool mybool = false;
     ^~~~
     _Bool
main.c:2:19: error: ‘false’ undeclared (first use in this function)
     bool mybool = false;
                   ^~~~~
main.c:2:19: note: each undeclared identifier is reported only once for each function it appears in

Solution:

Add

#include <stdbool.h>

at the top of the source file where the error occured.

The reason for this error is that bool is not a standard type in C (like int or char) but only in stdbool.h. Also, true and false are declared in stdbool.h.

Jun

2019

How to fix C error ‘true undeclared’

Problem:

You have C code like

bool mybool = true;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:2:5: error: unknown type name ‘bool’; did you mean ‘_Bool’?
     bool mybool = true;
     ^~~~
     _Bool
main.c:2:19: error: ‘true’ undeclared (first use in this function)
     bool mybool = true;
                   ^~~~
main.c:2:19: note: each undeclared identifier is reported only once for each function it appears in

Solution:

Add

#include <stdbool.h>

at the top of the source file where the error occured.

The reason for this error is that bool is not a standard type in C (like int or char) but only in stdbool.h. Also, true and false are declared in stdbool.h.

Jun

2019

How to fix C error ‘unknown type name bool’

Problem:

You have C code like

bool mybool;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:3:5: error: unknown type name ‘bool’; did you mean ‘_Bool’?
     bool mybool;
     ^~~~
     _Bool

Solution:

Add

#include <stdbool.h>

at the top of the source file where the error occured.

The reason for this error is that bool is not a standard type in C (like int or char) but only in stdbool.h.

Jun

2019

How to fix C error ‘NULL undeclared’

Problem:

You have C code like

char* ptr = NULL;

but when you try to compile it you see an error message like

main.c: In function ‘main’:
main.c:3:17: error: ‘NULL’ undeclared (first use in this function)
     void* ptr = NULL;
                 ^~~~
main.c:3:17: note: each undeclared identifier is reported only once for each function it appears in

Solution:

Add

#include <stddef.h>

at the top of the source file where the error occured.

The reason for this error is that NULL is not defined in C itself but only in stddef.h.

Jun

2019

How to get length of curve in OpenCASCADE

OCCUtils provides a convenience function to get the length of a curve in OpenCASCADE:

#include <occutils/Curve.hxx>

using namespace OCCUtils;

GeomAdaptor_Curve curve = /* ... */;

double length = Curve::Length(curve);

You can call it with GeomAdaptor_Curve or Geom_TrimmedCurve. While you can also call it with Handle(Geom_Curve), this is usually not what you want to do, since Geom_Curve typically describes an infinite curve (like an infinitely long line) and doesn’t know about which section of the curve is actually use (GeomAdaptor_Curve and Geom_TrimmedCurve both have the required Umin/Umax information stored).

In case you need to do it manually (without OCCUtils), use this snippet:

#include <GCPnts_AbscissaPoint.hxx>

GeomAdaptor_Curve curve = /* ... */;

GCPnts_AbscissaPoint::Length(curve);

For a Geom_TrimmedCurve, you need to convert it to a GeomAdaptor_Curve first. See How to convert Geom_TrimmedCurve to GeomAdaptor_Curve in OpenCASCADE for details on how to do that.

Jun

2019

How to convert Geom_TrimmedCurve to GeomAdaptor_Curve in OpenCASCADE

OCCUtils provides a conveniece function to convert a Geom_TrimmedCurve to a GeomAdaptor_Curve:

#include <occutils/Curve.hxx>

using namespace OCCUtils;

Geom_TrimmedCurve input = /* ... */;

GeomAdaptor_Curve result = Curve::FromTrimmedCurve(input);

If you want to do it manually, use this snippet:

Geom_TrimmedCurve input = /* ... */;

GeomAdaptor_Curve result(
    input.BasisCurve(), input.FirstParameter(), input.LastParameter()
);

Jun

2019

How to check if two gp_Pnt coincide in OpenCASCADE

If you have two points in OpenCASCADE:

gp_Pnt p1 = /* ... */;
gp_Pnt p2 = /* ... */;

you can’t just use == to check if they coincide in stock OpenCASCADE. However, OCCUtils provides operator== and operator!= for gp_Pnt among other types:

#include <occutils/Equality.hxx>

bool areTheyCoincident = p1 == p2;

If you can’t use OCCUtils, this is the way to check if they are coincident:

if (p1.Distance(p2) <= Precision::Confusion()) {
    // p1 coincides with p2
}

or alternatively:

if (p1.IsEqual(p2, Precision::Confusion())) {
    // p1 coincides with p2
}

The reason for this is that even though two points may represent the same point in space, depending on how you compute their coordinates exactly, their cartesian X/Y/Z coordinates might not be exactly identical. This is always the case with floating-point arithmetic, that’s the type of math computers use. Don’t confuse floating-point arithmetic with exact arithmetic which you have learnt in school or university.

The solution for this issue is to define a very small tolerance – any objects that have a distance less than that tolerance are considered equal.

In OpenCASCADE, Precision::Confusion() in the standard tolerance value for this.

My OCCUtils library provides

Jun

2019

How to create TopoDS_Edge from to gp_Pnt in OpenCASCADE

OCCUtils provides a conveniece function for creating a TopoDS_Edge between two points (i.e. a straight line):

#include <occutils/Edge.hxx>

using namespace OCCUtils;

gp_Pnt p1 = /* ... */;
gp_Pnt p2 = /* ... */;

TopoDS_Edge edge = Edge::FromPoints(p1, p2);

In case you want to do it manually (i.e. without OCCUtils), use this snippet

TopoDS_Edge edge = BRepBuilderAPI_MakeEdge(p1, p2).Edge();

but be aware that you also have to handle the case of p1 == p2 i.e.

if (p1.Distance(p2) <= Precision::Confusion()) {
    // Don't try to create an Edge in this case
}

OCCUtil’s Edge::FromPoints handles this case by returning TopoDS_Edge() i.e. a TopoDS_Edge where edge.IsNull() == true.

Jun

2019

How to fix boost::program_options “error: ‘po’ has not been declared”

If you want to compile your C++ project using boost::program_options but you see error messages like

/home/uli/myProject/main.cpp:28:5: error: ‘po’ has not been declared
     po::notify (vm);

you are missing this declaration which you need to place directly after #include <boost/program_options.hpp>:

namespace po = boost::program_options;

This declares po as an alias for the boost::program_options namespace, because writing po::variables_map is much easier to read than boost::program_options::variables_map and using namespace boost::program_options might cause some name collisions with other functions.

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Search

Categories